Most of my Neptun conversions up have up to now been USN or RN. There are two good reasons for this. First, much more is known about what different class-sisters in the Allied navies looked like at different points in their careers than their Axis counterparts. Second, the fact that Neptun has made many of the USN and RN DD types in both "as-built" and late war configuration means that swapping parts like AA mounts and torpedo tubes from one to another to create new variants is straightforward. Not so for the Imperial Japanese Navy (IJN). Documentation on individual class variations is slim and comparatively few photographs are readily available. And most of the IJN destroyer types that Neptun produces are issued only in as-built configuration. This means that any additional detail must be constructed from scratch.
Despite these challenges, converting IJN Neptuns can be fruitful. Because the Japanese took the opportunity to add AA and make other modifications any time a unit experienced a significant yard period, there was little standardization in how this occurred. Many of the DD types lost X mount in favor of two triple 25mm AA mounts (as illustrated by N1268a Uranami). But numerous single 25mm mounts were frequently added as well. Radar, supported by heavier foremasts, was also added as it became available. So by 1944 or so, very few surviving sisters were identical.
Ferreting out these details is rewarding, but can be difficult. Documentation is scarce and published sources sometimes disagree. For armament information, the best source is the general arrangement drawings prepared by Shizuo Fukui during the war, based on actual observation. These are available in several publications, but I have found the best way to obtain them—as well as savor the latest information and controversies on the IJN—is to post questions on the j-aircraft board at http://www.j-aircraft.org/smf/index.php?board=16.0. The people who haunt this board are incredibly knowledgeable and helpful. But even with their help, I have sometimes had to be satisfied with less certainty about a particular conversion than I would like.
Yamagumo in 1944 illustrates the basic IJN late-war DD AA fit applied to most of the survivors of the Asashio and Kagero classes. X mount is landed and two triple 25mm are substituted in super-firing positions. Because of the position of the mainmast and the torpedo reload gear, these are offset from the center line. The triple 25mms are scratch-built using plastic for the mounting itself and brass wire for the barrels. The tubs for them are built up from plastic with shielding made from sheet copper. Additional single 25mm mounts are added forward and aft, following a Fukui drawing. Occasionally, these are arranged asymmetrically, with a different number of mounts on one side of the ship than the other. The single 25mms are simply a plastic dowel sunk into the deck, topped with a brass wire. The mast is a rework of the original, achieved by splitting the tripod apart and adding a plastic top and topmast, as well as radar. She also lost a pair of boats abreast the forward superstructure.
Katzagumo illustrates the many "urban legends" that surround IJN modifications. It is widely believed, and is reported in some standard publications, that the Yugumos and Shimekaze also had X mount removed. But photographic evidence contradicts this. Instead, additional triple 25mm mounts were added on elevated platforms abreast of the forward funnel. At the same time, the twin mounts abreast of the second funnel were upgraded to triples. The forward AA mount remained a twin. This configuration is best illustrated in Warship International, Volume 41, Issue 3, p.273 which I used as the primary guide.
Tameichi Hara’s Shigure provides a legendary subject for the smaller 1600-tonners. The removal of the single 5" in X position only leaves room for one triple 25mm mount on a raised platform. A twin 25mm is carried in a new tub forward of the bridge and the twins abreast the after funnel are replaced by triples. All the rest of the 25mm are singles. The usual modification of the tripod and addition of radars complete the conversion. All documentation on this was from Fukui, via the j-board.
The IJN did not make much use of camouflage, with the exception of the Aleutian campaigns. But the j-board recently discussed a camouflage scheme briefly carried by the Mutsukis in mid-1941, illustrated on Jon Parshall’s web page (http://www.combinedfleet.com/mutsuk_c.htm). Modifications here were minimal, but included mounting a twin 25mm in place of the amidships searchlight and single 13mm mounts on either side of the bridge at the back of the forward torpedo well.
The modifications to the Mutsukis turn out to be among the murkiest applied to IJN DDs during the war because few plans and almost no photographs exist. Many myths have therefore resulted. One example is the reasonable, but incorrect, belief that the two 4.7" mounts were retained fore and aft. Actually, this modification involved keeping #1 mount forward and #3 amidships. The after funnel also needed to be cut down because the transport modification cut out a boiler room. There is a well-known photo of Nagatsuki under air attack that has this narrow funnel, and I used it as the basis for the conversion. Triple 25mm mounts were also added amidships and aft. The most controversial feature is the pair of Daihatsu landing craft with associated davits. The photo stimulated a big debate on the j-board because it appears to show these davits and some neat photo-manipulation by Ed Low proved that there was room for a Daihatsu. The idea was sufficiently cool that I decided to take the risk.
The torpedo-boats also provide fruitful subjects for conversion because not a lot needs to be done. Kiji illustrates a typical late-war anti-submarine fit, with one 4.7" mount landed in favor a triple 25mm and numerous single 25mm, plus radar and enhanced depth charge capacity. This was my first IJN conversion, based on the little information available in published sources before I discovered the j-board.
Neptun has begun to pay attention to variations across the IJN heavy cruiser classes, some of which are portrayed in late-war format. But with the exception of the excellent Isuzu as an AA cruiser (N1245a), all the CLs are modeled as-built. This provides ample room for conversion. For example, the Katoris were chiefly used as escort group flagships in the last two years of the war, and were heavily modified. My version of Kashima involved landing the torpedo tubes in favor of two additional scratch-built twin 5" AA mounts, as well as added triple 25mm in tubs amidships and on the after superstructure. Radar was added as well. This conversion also taught me a lesson about consistent look-and-feel because the two scratch-built 5" mounts didn’t look right alongside the original 5" mount aft. So I decided to make three that matched and get rid of the original!
This set me up for the only IJN opportunity to swap parts that I have so far experienced, because I now had a perfectly good twin 5" AA mount. I knew from my Konishi model of Nagara that many of the CLs landed a 5.5" mount aft and substituted a twin 5" AA. So I looked for a Kuma in this configuration. Kiso in 1944 was the result. In addition to the 5" AA substitution, this conversion involved getting rid of the catapult and several boats, the addition of many triple, twin, and single 25mm mounts, as well as radar. I am once again indebted to the folks on the j-board for providing me with general arrangement drawings.
Accurate conversion of IJN subjects is a good deal more uncertain than for Allied navies because of spotty documentation. So instead of deliberately deciding to do a particular ship and looking for the information that I need, I generally lurk on the j-board until something reasonably well documented comes up. But the uncertainty is worth it because many interesting and unexpected things result. Once again, I urge you to give it a try!